<!doctype html>
<html>
	<head>
		<meta charset="utf-8">
		<meta name="viewport" content="width=device-widht,initial-scale=1,mximum-scale=1,user-scalable=no">
		<title></title>
		<link rel="stylesheet" href="css/bootstrap.min.css">
	</head>
	<style>
		#dv{
			font-size:14px;
			border: 1px solid #ff0000;
		}
		@media screen and (min-width: 400px){
			#dv{
				font-size:12px;
				border: 1px solid #00ff00;
			}
		}
		@media screen and (max-width:600px){
			#dv{
				font-size:16px;
				border: 1px solid #0000ff;
			}
		}
	</style>
	<body>
		<div id="dv">
			aaa
		</div>
	</body>
</html>